1. Field of the Invention
The present invention relates to an ultrasonic probe, an ultrasonic receiver, and an ultrasonic diagnostic apparatus for performing medical diagnosis by receiving ultrasonic waves through the use of the foregoing ultrasonic probe and ultrasonic receiver.
2. Description of a Related Art
Conventionally, when acquiring a three-dimensional image through the use of ultrasonic waves, a plurality of two-dimensional images of sections in a direction of depth have been obtained and synthesized. These two-dimensional images can be obtained by scanning a one-dimensional sensor array fitted with a position sensor, and further a three-dimensional image can be obtained by synthesizing the plurality of two-dimensional images which were obtained in time series.
In this technique, however, a time lag exists in a scanning direction of the one-dimensional sensor array and therefore the sectional images generated at different times are synthesized, whereby the resultant synthetic image becomes out of focus. Accordingly, such approach is not suitable for imaging of an object like a living body which is accompanying some movement.
In order to obtain a three-dimensional image in real time, it is essential to provide a two-dimensional sensor array which can obtain a two-dimensional image without putting a sensor array into scanning operation, and there is thus a need of developing such a sensor array.
In an ultrasonic diagnostic apparatus, piezoelectric ceramics represented by PZT (Pb (lead) zirconate titanate) and polymer piezoelectric elements such as PVDF (polyvinyl difluoride) piezoelectric polymer are typically used as an element (oscillator or probe) for transmitting and/or receiving ultrasonic waves, and a technique for fabricating a two-dimensional array incorporating these elements is now under examination. However, using the PZT or PVDF as mentioned above requires microfabrication of the elements and wiring to a large number of microcomponents, and it is difficult to increase the fineness and integration of the elements beyond those possible in the present state. Even if these difficulties are solved, however, there remain such problems that crosstalk between the elements increases, and that a rise in electrical impedance caused by such fine wiring deteriorates a signal-to-noise ratio and increases the susceptibility of a microcomponent at an electrode part to fracture, which makes the implementation of such a two-dimensional sensor array using PZT or PVDF difficult.
For example, ULTRASONIC IMAGING 20, 1-15 (1998) carries a paper entitled xe2x80x9cProgress in Two-Dimensional Arrays for Real-Time Volumetric Imagingxe2x80x9d by E. D. LIGHT et al., Duke University. This paper discloses a probe comprising a two-dimensional array of PZT ultrasonic sensors. This paper, however, concurrently describes as follows: xe2x80x9cTo make similar quality images, two dimensional array would require 128xc3x97128=16,384 elements. Because of the cost and complexity of building such a large number of RF channels, it is unlikely that anyone will construct such an ultrasonic imaging system in the near future. Also, connecting to so many elements in such a dense aperture is very difficult. (page 2, lines 14-18).xe2x80x9d
On the other hand, a sensor incorporating an optical fiber has been applied to an ultrasonic sensor without the use of any piezoelectric materials such as PZT. As such optical fiber ultrasonic sensors, there have been reported those incorporating a fiber Bragg grating (abbreviated as FBG) (see the paper Takahashi et al., Japan Defense Academy, xe2x80x9cUnderwater Acoustic Sensor with Fiber Bragg Gratingxe2x80x9d, OPTICAL REVIEW Vol. 4, No. 6 (1997) pp. 691-694) and those incorporating a Fabry-Perot resonator (abbreviated as FPR) structure (see the paper Uno et. al., Tokyo Institute of Technology xe2x80x9cFabrication and Performance of a Fiber Optic Micro-Probe for Megahertz Ultrasonic Field Measurementsxe2x80x9d T. IEE Japan, Vol. 118-E, NO.11, ""98), all of which are discrete sensors, and the idea of forming a sensor array composed of such sensors has not been reported.
Also, the above-mentioned document written by TAKAHASHI et al. describes that these sensors may have certain sensitivities with respect to such ultrasonic waves having relatively low frequency ranges, e.g., on the order of 20 kHz. However, no description is made as to such ultrasonic waves operable in megahertz-order frequency ranges which are used in the actual ultrasonic diagnoses. As a consequence, in order to practically use these sensors, sensor operations with respect to ultrasonic waves having higher frequency ranges than those of the described examples are necessarily confirmed. Furthermore, conditions should be researched, if required, under which better sensor sensitivities could be obtained in such high frequency ranges.
The present invention is provided in view of the aforementioned problems. The first object of the present invention is to provide an ultrasonic probe comprising a sensor array which does not require electric wiring to a large number of microcomponents and does not induce increase of crosstalk and electric impedance. The second object of the present invention is to provide an ultrasonic receiver which can obtain a three-dimensional image data without scanning the probe. Further, the third object of the present invention is to provide an ultrasonic diagnostic apparatus using such an ultrasonic probe and ultrasonic receiver.
To solve the problems mentioned above, an ultrasonic probe according to the present invention comprises: an optical transmission path array including a plurality of optical transmission paths on which light is incident at first ends thereof; and a plurality of ultrasonic detecting elements, formed at second ends of the plurality of optical fibers and modulate the light coming through the respective optical fibers depending on an applied ultrasonic wave.
Further, an ultrasonic receiver according to the present invention comprises: a plurality of ultrasonic detecting elements which are arranged in the form of two-dimensional array and modulate light depending on an applied ultrasonic wave; and a photodetector for detecting light emerging from the plurality of ultrasonic detecting elements.
Still further, an ultrasonic diagnostic apparatus in according to the present invention comprises: a drive signal generating circuit for generating a drive signal to transmit ultrasonic waves; an ultrasonic transmission unit for transmitting ultrasonic waves to an object in response to the drive signal supplied from the drive signal generating circuit; an ultrasonic detection unit including a plurality ultrasonic detecting elements for selectively reflecting light, each of said plurality of ultrasonic detecting elements for modulating light depending on ultrasonic waves applied thereto; a photodetector for detecting the light output from the ultrasonic detection unit to generate a detection signal; signal processing means for processing the detection signal supplied from the photodetector; and control means for controlling transmission timing of the drive signal generating circuit and receive timing of the signal processing means.
According to the present invention light is used for detecting ultrasonic waves, and therefore, there is no need for electric wiring to a large number of microcomponents and crosstalk and increase in electric impedance are not caused. Thus, an ultrasonic probe and ultrasonic receiver both of which are easy to manufacture and provide a good SN ratio, and an ultrasonic diagnostic apparatus using them can be implemented.